The field of the disclosure relates generally to components having an internal passage defined therein, and more particularly to defining such internal passages using cores that define at least one of a large length-to-diameter ratio, a substantially nonlinear shape, and a complex cross-sectional perimeter.
Some components require an internal passage to be defined therein, for example, in order to perform an intended function. For example, but not by way of limitation, some components, such as hot gas path components of gas turbines, are subjected to high temperatures. At least some such components have internal passages defined therein to receive a flow of a cooling fluid, such that the components are better able to withstand the high temperatures. For another example, but not by way of limitation, some components are subjected to friction at an interface with another component. At least some such components have internal passages defined therein to receive a flow of a lubricant to facilitate reducing the friction.
At least some known components having an internal passage defined therein are formed in a mold, with a core of ceramic material extending within the mold cavity at a location selected for the internal passage. After a molten metal alloy is introduced into the mold cavity around the ceramic core and cooled to form the component, the ceramic core is removed, such as by chemical leaching, to form the internal passage. However, at least some known ceramic cores are fragile, resulting in cores that are difficult and expensive to produce and handle without damage. As just one non-limiting example, as a length-to-diameter (L/d) ratio of the ceramic core increases, the risk of cracking or breaking of the core during handling and/or use in production of a component also increases.
The risk of cracking or breaking of at least some such ceramic cores is further increased as a non-linearity of the ceramic core increases. For example, a substantially linear ceramic core can be aligned with a direction of gravity such that the core supports its own weight in columnar compression. In contrast, when a substantially non-linear core is suspended within a mold cavity, the weight of the core subjects at least a portion of the ceramic core to tension, which further increases the risk of cracking or breaking of the ceramic core. Additionally or alternatively, at least some such cores are themselves produced by casting the ceramic material in a core mold, and at least some substantially non-linear ceramic cores are difficult to produce due to a difficulty in providing suitable pull planes and draft angles for release of the non-linear ceramic core from the core mold. Thus, a use of such known ceramic cores to define internal passages having substantial non-linearity is limited, particularly, but not limited to, as the L/d ratio of the passage increases.
Additionally, the risk of cracking or breaking of at least some such ceramic cores is increased as a complexity of a cross-section of the ceramic core increases. As just one non-limiting example, a non-smooth cross-sectional perimeter introduces stress concentrations in the ceramic core that increase a risk of local cracking. Thus, for example, while a heat-transfer performance of an internal cooling passage might be improved by a cross-section that increases a wetted perimeter of the passage for a given cross-sectional area, a use of such known ceramic cores to define such a cross-section is limited, particularly, but not limited to, as the L/d ratio of the passage increases.
Alternatively or additionally, at least some known components having an internal passage defined therein are initially formed without the internal passage, and the internal passage is formed in a subsequent process. For example, at least some known internal passages are formed by drilling the passage into the component, such as, but not limited to, using an electrochemical drilling process. However, at least some such processes are relatively time-consuming and expensive. Moreover, at least some such processes cannot produce an internal passage non-linearity and/or cross-sectional perimeter required for certain component designs, particularly, but not limited to, as the L/d ratio of the passage increases.